U.S. patent number 5,801,508 [Application Number 08/691,592] was granted by the patent office on 1998-09-01 for apparatus for controlling a polyphase ac motor in quick-torque and high-efficiency modes.
This patent grant is currently assigned to Nippondenso Co., Ltd.. Invention is credited to Kazuyoshi Obayashi.
United States Patent |
5,801,508 |
Obayashi |
September 1, 1998 |
Apparatus for controlling a polyphase AC motor in quick-torque and
high-efficiency modes
Abstract
An inverter circuit includes a plurality of sets each having a
series combination of two switching elements. Two ends of each of
the sets are connected to a vehicle battery. A junction between the
two switching elements in each of the sets is electrically
connected to a polyphase ac motor. A vector controller is operative
for controlling the inverter circuit on the basis of a
torque-current command value and a magnetizing-current command
value. The vector controller includes a command value calculating
device for calculating a motor-torque command value on the basis of
a required torque, and an operation mode judging device for judging
an operation mode to be a quicker-torque-response mode or a
higher-efficiency mode on the basis of various conditions. The
vector controller also includes a first calculating device for, in
cases where the operation mode judging device judges the operation
mode to be the higher-efficiency mode, calculating the
magnetizing-current command value and the torque-current command
value, which maximizes an energy efficiency, on the basis of the
motor-torque command value. The vector controller further includes
a second calculating device for, in cases where the operation mode
judging device judges the operation mode to be the
quicker-torque-response mode, fixing the magnetizing-current
command value to a present value thereof or a given value and
calculating the torque-current command value from the fixed
magnetizing-current command value and the motor-torque command
value.
Inventors: |
Obayashi; Kazuyoshi (Kariya,
JP) |
Assignee: |
Nippondenso Co., Ltd. (Kariya,
JP)
|
Family
ID: |
16409473 |
Appl.
No.: |
08/691,592 |
Filed: |
August 2, 1996 |
Foreign Application Priority Data
|
|
|
|
|
Aug 4, 1995 [JP] |
|
|
7-199536 |
|
Current U.S.
Class: |
318/801;
318/139 |
Current CPC
Class: |
B60L
15/025 (20130101); Y02T 10/64 (20130101); Y02T
10/643 (20130101) |
Current International
Class: |
B60L
15/00 (20060101); B60L 15/02 (20060101); H02P
007/00 () |
Field of
Search: |
;318/139,798-822,611
;363/41,56 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Fetz et al; High Efficiency Induction Motor Drive with Good Dynamic
Performance for Electric Vehicles, 1993, pp. 1-7. .
Mizuno et al; "Comparison of Characteristics of an Induction Motor
and a Permanent-Magnet Motor in a State of Constant-Output
Operation", pp. 1-10 with Partial English Translation,
1993..
|
Primary Examiner: Wysocki; Jonathan
Attorney, Agent or Firm: Cushman Darby & Cushman IP
Group of Pillsbury Madison & Sutro LLP
Claims
What is claimed is:
1. A control apparatus for a polyphase ac motor, comprising:
a battery;
an inverter circuit, connected to the battery, said inverter
including a plurality of sets of switches, each of said sets of
switches having a series combination of two switching elements,
wherein two ends of each of said sets of switches are connected to
the battery, and a junction between the two switching elements in
each of said sets of switches is electrically connected to a
respective terminal of the polyphase ac motor; and
a vector controller for controlling the inverter circuit on the
basis of a torque-current command value and a magnetizing-current
command value;
wherein the vector controller comprises:
a) command value calculating means for calculating a motor-torque
command value on the basis of a required torque such as a degree of
depression of an accelerator pedal;
b) operation mode judging means for judging an operation mode to be
a quicker-torque-response mode or a higher-efficiency mode, the
quicker-torque-response mode having quicker torque response than
the higher-efficiency mode, the higher-efficiency mode having
higher energy efficiency than the quicker-torque-response mode;
c) first calculating means for, in cases where the operation mode
judging means judges the operation mode to be the higher-efficiency
mode, calculating the magnetizing-current command value and the
torque-current command value, which maximizes an energy efficiency,
on the basis of the motor-torque command value; and
d) second calculating means for, in cases where the operation mode
judging means judges the operation mode to be the
quicker-torque-response mode, fixing the magnetizing-current
command value to a present value thereof and calculating the
torque-current command value from the fixed magnetizing-current
command value and the motor-torque command value.
2. A control apparatus as recited in claim 1, wherein the command
value calculating means is operative for calculating the
motor-torque command value in view of measured values of currents
flowing through the polyphase ac motor, a voltage across the
battery, a rotational speed of the polyphase ac motor, and voltages
among different terminals of the polyphase ac motor.
3. A control apparatus as recited in claim 1, wherein the operation
mode judging means is operative for judging the operation mode to
be the quicker-torque-response mode when a rate of a variation in
the motor-torque command value calculated by the command value
calculating means is greater than a threshold value, and is
operative for judging the operation mode to be the
higher-efficiency mode when the rate of the variation in the
motor-torque command value calculated by the command value
calculating means is smaller than said threshold value.
4. A control apparatus as recited in claim 1, further comprising a
mode selection switch for manually selecting one out of the
quicker-torque-response mode and the higher-efficiency mode,
wherein the operation mode judging means is operative for judging
the operation mode to be the quicker-torque-response mode when the
quicker-torque-response mode is selected by the mode selection
switch, and is operative for judging the operation mode to be the
higher-efficiency mode when the higher-efficiency mode is selected
by the mode selection switch.
5. A control apparatus as recited in claim 1, further comprising
remaining energy detecting means for detecting an amount of
electric energy remaining in the battery, wherein the operation
mode judging means is operative for judging the operation mode to
be the higher-efficiency mode when the detected amount of electric
energy remaining in the battery is less than a given value.
6. A control apparatus as recited in claim 1, wherein the first
calculating means is further for low pass filtering the
magnetizing-current command value.
7. A control apparatus as recited in claim 1, wherein the first
calculating means is further for low pass filtering the
magnetizing-current command value and the torque-current command
value.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a control apparatus for a polyphase ac
(alternating current) motor usable in, for example, an electric
vehicle.
2. Description of the Prior Art
A known way of varying the torque of a polyphase ac motor is to
increase or decrease a torque current while maintaining a
magnetizing current at a constant level. This known way enables the
torque response characteristics of the polyphase ac motor to be
comparable to those of a dc motor.
Some electric vehicles use a polyphase ac motor as a drive power
source. A known technique for enhancing the energy efficiency
during the travel of such an electric vehicle has a step of
deriving a command value of a motor torque from the degree of
depression of an accelerator pedal, a step of calculating a command
value of a torque current and a command value of a magnetizing
current from the motor-torque command value, and a step of
subjecting the polyphase ac motor to vector control responsive to
the torque-current command value and the magnetizing-current
command value. The calculation of the torque-current command value
and the magnetizing-current command value is executed by referring
to a map providing a predetermined relation among the motor-torque
command value, the torque-current command value, and the
magnetizing-current command value.
In the case where the previously-indicated known way is applied to
an electric vehicle powered by a polyphase ac motor, the energy
efficiency tends to be low and every full charging of a vehicle
battery tends to enable only a short distance traveled by the
vehicle.
According to the previously-indicated known technique, both an
actual magnetizing current and an actual torque current vary as the
motor-torque command value changes. The actual torque approximately
follows the motor-torque command value. On the other hand, the
magnetic flux caused by the actual magnetizing current slowly
varies due to the influence of the second-order time constant of
the polyphase ac motor. An actual motor torque is proportional to
the product of the actual torque current and the magnetic flux.
Therefore, the slow variation of the magnetic flux results in a
slow response of the actual motor torque to the motor-torque
command value. Thus, the electric vehicle tends to exhibit a poor
acceleration response to the depression of the accelerator
pedal.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved control
apparatus for a polyphase ac (alternating current) motor usable in,
for example, an electric vehicle.
A first aspect of this invention provides a control apparatus for a
polyphase ac motor which comprises a vehicle battery; an inverter
circuit connected to the vehicle battery and including a plurality
of sets each having a series combination of two switching elements,
wherein two ends of each of said sets are connected to the vehicle
battery, and a junction between the two switching elements in each
of said sets is electrically connected to the polyphase ac motor;
and a vector controller for controlling the inverter circuit on the
basis of a torque-current command value and a magnetizing-current
command value; wherein the vector controller comprises a) command
value calculating means for calculating a motor-torque command
value on the basis of a required torque such as a degree of
depression of an accelerator pedal; b) operation mode judging means
for judging an operation mode to be a quicker-torque-response mode
or a higher-efficiency mode on the basis of various conditions, the
quicker-torque-response mode attaching importance to torque
response, the higher-efficiency mode attaching importance to energy
efficiency; c) first calculating means for, in cases where the
operation mode judging means judges the operation mode to be the
higher-efficiency mode, calculating the magnetizing-current command
value and the torque-current command value, which maximizes an
energy efficiency, on the basis of the motor-torque command value;
and d) second calculating means for, in cases where the operation
mode judging means judges the operation mode to be the
quicker-torque-response mode, fixing the magnetizing-current
command value to a present value thereof or a given value and
calculating the torque-current command value from the fixed
magnetizing-current command value and the motor-torque command
value.
A second aspect of this invention is based on the first aspect
thereof, and provides a control apparatus wherein the command value
calculating means is operative for calculating the motor-torque
command value in view of measured values of currents flowing
through the polyphase ac motor, a voltage across the vehicle
battery, a rotational speed of the polyphase ac motor, and voltages
among different phases of the polyphase ac motor.
A third aspect of this invention is based on the first aspect
thereof, and provides a control apparatus wherein the operation
mode judging means is operative for judging the operation mode to
be the quicker-torque-response mode when a rate of a variation in
the motor-torque command value calculated by the command value
calculating means is great, and is operative for judging the
operation mode to be the higher-efficiency mode when the rate of
the variation in the motor-torque command value calculated by the
command value calculating means is small.
A fourth aspect of this invention is based on the first aspect
thereof, and provides a control apparatus further comprising a mode
selection switch for manually selecting one out of the
quicker-torque-response mode and the higher-efficiency mode,
wherein the operation mode judging means is operative for judging
the operation mode to be the quicker-torque-response mode when the
quicker-torque-response mode is selected by the mode selection
switch, and is operative for judging the operation mode to be the
higher-efficiency mode when the higher-efficiency mode is selected
by the mode selection switch.
A fifth aspect of this invention is based on the first aspect
thereof, and provides a control apparatus further comprising
remaining energy detecting means for detecting an amount of
electric energy remaining in the vehicle battery, wherein the
operation mode judging means is operative for judging the operation
mode to be the higher-efficiency mode when the detected amount of
electric energy remaining in the vehicle battery is small.
A sixth aspect of this invention is based on the first aspect
thereof, and provides a control apparatus further comprising a low
pass filter processing the magnetizing-current command value.
A seventh aspect of this invention is based on the first aspect
thereof, and provides a control apparatus further comprising low
pass filters processing the magnetizing-current command value and
the torque-current command value respectively.
An eighth aspect of this invention provides a control apparatus for
a polyphase ac motor which comprises first means for setting a
fixed desired magnetizing current; second means for setting a
desired torque current in response to a required torque output of
the motor and the fixed desired magnetizing current set by the
first means; and third means for supplying the motor with an actual
magnetizing current and an actual torque current corresponding to
the fixed desired magnetizing current set by the first means and
the desired torque current set by the second means
respectively.
A ninth aspect of this invention provides a control apparatus for a
polyphase ac motor which comprises first means for changing
operation of the motor between a first mode and a second mode;
second means for setting a first desired magnetizing current and a
first desired torque current in response to a required torque
output of the motor in cases where the operation of the motor is in
the first mode; third means for supplying the motor with an actual
magnetizing current and an actual torque current corresponding to
the first desired magnetizing current and the first desired torque
current set by the second means respectively in cases where the
operation of the motor is in the first mode; fourth means for
setting a second desired magnetizing current which is fixed in
cases where the operation of the motor is in the second mode; fifth
means for setting a second desired torque current in response to a
required torque output of the motor and the second desired
magnetizing current set by the fourth means in cases where the
operation of the motor is in the second mode; and sixth means for
supplying the motor with an actual magnetizing current and an
actual torque current corresponding to the second desired
magnetizing current set by the fourth means and the second desired
torque current set by the fifth means respectively in cases where
the operation of the motor is in the second mode.
A tenth aspect of this invention is based on the ninth aspect
thereof, and provides a control apparatus wherein the first means
comprises means for deciding whether or not a rate of a variation
in the required torque output of the motor exceeds a predetermined
threshold value, means for changing the operation of the motor to
the second mode when the deciding means decides that the rate of
the variation exceeds the threshold value, and means for changing
the operation of the motor to the first mode when the deciding
means decides that the rate of the variation does not exceed the
threshold value.
An eleventh aspect of this invention is based on the ninth aspect
thereof, and provides a control apparatus wherein the first means
comprises a manual switch changeable between a first position and a
second position, means for changing the operation of the motor to
the first mode when the manual switch assumes the first position,
and means for changing the operation of the motor to the second
mode when the manual switch assumes the second position.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of a control apparatus for a three-phase ac
motor according to a first embodiment of this invention.
FIG. 2 is a diagram of an ECU (electronic control unit) and related
parts in the control apparatus of FIG. 1.
FIG. 3 is a flowchart of a first segment of a control program for
the ECU in FIGS. 1 and 2.
FIG. 4 is a diagram of a predetermined map in the control apparatus
of FIG. 1 which provides a relation between a motor-torque command
value and a torque-current command value, and also a relation
between the motor-torque command value and a magnetizing-current
command value.
FIG. 5 is a flowchart of a second segment of the control program
for the ECU in FIGS. 1 and 2.
FIG. 6 is a time-domain diagram of various parameters in the
control apparatus and the three-phase ac motor in FIG. 1.
FIG. 7 is a time-domain diagram of various parameters in a
prior-art control apparatus and a three-phase ac motor.
FIG. 8 is a time-domain diagram of various parameters in a control
apparatus and a three-phase ac motor according to a seventh
embodiment of this invention.
FIG. 9 is a flowchart of a segment of a control program for an ECU
in an eighth embodiment of this invention.
FIG. 10 is a flowchart of a segment of a control program for an ECU
in a ninth embodiment of this invention.
FIG. 11 is a flowchart of a segment of a control program for an ECU
in a tenth embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
With reference to FIG. 1, a control apparatus "A" operates on a
three-phase ac (alternating current) motor 3. The control apparatus
"A" is placed in an electric vehicle (not shown). The control
apparatus "A" includes a vehicle battery 1, an inverter circuit 2,
and an ECU (electronic control unit) 4. The inverter circuit 2 is
connected to the vehicle battery 1, the three-phase ac motor 3, and
the ECU 4. Current sensors 311 and 331 are provided on the
connection between the inverter circuit 2 and the three-phase ac
motor 3. The current sensors 311 and 331 are connected to the ECU 4
via a current detection circuit 30 such as an amplifier. The ECU 4
controls the inverter circuit 2 in response to the output signals
of the current detection circuit 30. The ECU 4 includes, for
example, a microcomputer or a similar device having a combination
of an input/output port, a processing section, a RAM, and a ROM.
The ECU 4 operates in accordance with a program stored in the
ROM.
The vehicle battery 1 includes, for example, a lead battery. The
vehicle battery 1 stores electric power for driving the three-phase
ac motor 3 or others.
The inverter circuit 2 includes IGBT's (insulated gate bipolar
transistors) 21, 22, 23, 24, 25, and 26, and a smoothing capacitor
27. The smoothing capacitor 27 is connected across the vehicle
battery 1. The source-drain paths of the IGBT's 21 and 22 are
connected in series. The series combination of the IGBT's 21 and 22
is connected across the vehicle battery 1. The source-drain paths
of the IGBT's 23 and 24 are connected in series. The series
combination of the IGBT's 23 and 24 is connected across the vehicle
battery 1. The source-drain paths of the IGBT's 25 and 26 are
connected in series. The series combination of the IGBT's 25 and 26
is connected across the vehicle battery 1.
The three-phase ac motor 3 is a power source for driving the
electric vehicle. The three-phase ac motor 3 has three stator
windings corresponding to three different phases respectively. The
first stator winding of the motor 3 is connected via a connection
line 31 to the junction 210 between the IGBT's 21 and 22. The
second stator winding of the motor 3 is connected via a connection
line 32 to the junction 230 between the IGBT's 23 and 24. The third
stator winding of the motor 3 is connected via a connection line 33
to the junction 250 between the IGBT's 25 and 26.
The ECU 4 has three output terminals. The first output terminal of
the ECU 4 is connected to the gate of the IGBT 21. The first output
terminal of the ECU 4 is connected via an inverter (no reference
character) to the gate of the IGBT 22. The second output terminal
of the ECU 4 is connected to the gate of the IGBT 23. The second
output terminal of the ECU 4 is connected via an inverter (no
reference character) to the gate of the IGBT 24. The third output
terminal of the ECU 4 is connected to the gate of the IGBT 25. The
third output terminal of the ECU 4 is connected via an inverter (no
reference character) to the gate of the IGBT 26.
The ECU 4 serves as a vector controller. As shown in FIG. 2, the
ECU 4 includes a signal input section 41, a measured value input
section 42, an MPU (microprocessor unit) 43, a switch input section
44, and a switching pattern output section 45. The MPU 43 operates
in accordance with a program stored in its internal ROM. The MPU 43
serves as a command value calculating means 431, an operation mode
judging means 432, a first calculating means 433, a second
calculating means 434, and a vector control calculating means
435.
With reference to FIG. 1, the electric vehicle has an accelerator
pedal 50. A position sensor 51 connected to the accelerator pedal
50 outputs an accelerator position signal representing the degree
of depression of the accelerator pedal 50, that is, a required
torque output of the three-phase ac motor 3.
With reference to FIG. 2, the signal input section 41 receives the
accelerator position signal from the accelerator position sensor 51
(see FIG. 1) as an indication of the required torque. The signal
input section 41 includes, for example, an A/D converter. The
signal input section 41 converts the accelerator position signal
into a version which can be handled by the MPU 43. The signal input
section 41 feeds the resultant signal to the MPU 43. It should be
noted that a brake pedal position signal representing the degree of
depression of a vehicle brake pedal (not shown) may also be used as
an indication of the required torque.
As shown in FIG. 1, the current sensor 311 is associated with the
connection line 31 between the inverter circuit 2 and the
three-phase ac motor 3 to detect a current flowing along the
connection line 31. The current sensor 331 is associated with the
connection line 33 between the inverter circuit 2 and the
three-phase ac motor 3 to detect a current flowing along the
connection line 33. Thus, the current sensors 311 and 331 detect
currents fed from the inverter circuit 2 to the related stator
windings of the three-phase ac motor 3 respectively. The current
detection circuit 30 receives the output signals of the current
sensors 311 and 331, and suitably processes the received signals.
The current detection circuit 30 outputs the resultant signals to
the ECU 4 as an indication of measured current values.
With reference to FIG. 2, the measured value input section 42
receives the output signals of the current detection circuit 30 as
an indication of the measured current values. The measured value
input section 42 includes, for example, an A/D converter. The
measured value input section 42 converts the received signals into
versions which can be handled by the MPU 43. The measured value
input section 42 feeds the resultant signals to the MPU 43. It
should be noted that a signal representing a measured value of the
voltage across the vehicle battery 1, a signal representing a
measured rotational speed of the three-phase ac motor 3 (an output
signal of an encoder or a resolver), and signals representing
measured values of the voltages among the connection lines 31, 32,
33 may also be inputted.
The electric vehicle is provided with an operation mode selection
switch 441 and a manual switch 442. Operation of the electric
vehicle can be changed among different modes. During manual
operation of the electric vehicle, the operation mode can be
changed by the operation mode selection switch 441. The operation
mode selection switch 441 can be changed between first and second
positions which correspond to a quicker-torque-response mode and a
higher-efficiency mode respectively. The quicker-torque response
mode attaches importance to torque response. The higher-efficiency
mode attaches importance to energy efficiency. During automatic
operation of the electric vehicle, the operation mode can be
automatically changed between the quicker-torque response mode and
the higher-efficiency mode in response to a condition of a
motor-torque command value. The manual switch 442 serves to select
one out of the manual operation and the automatic operation. The
manual switch 442 can be changed between an on position and an off
position. When the manual switch 442 is in its off position, the
automatic operation is selected. When the manual switch 442 is in
its on position, the manual operation is selected.
The switch input section 44 receives the output signals of the
operation mode selection switch 441 and the manual switch 442. The
switch input section 44 includes, for example, buffer circuits. The
switch input section 44 transmits the output signals of the
switches 441 and 442 to the MPU 43.
The switching pattern output section 45 receives an output signal
403 of the MPU 43 which represents command voltages corresponding
to a magnetizing-current command value 401 and a torque-current
command value 402. The switching pattern output section 45
generates three switching command signals 404 in response to the
command voltages, and outputs the switching command signals 404 to
the inverter circuit 2.
The MPU 43 periodically calculates a motor-torque command value by
referring to the output signal of the signal input section 41 which
represents the required torque. This process implemented by the MPU
43 corresponds to the command value calculating means 431.
In the case where the MPU 43 detects from the output signal of the
switch input section 44 that the manual switch 442 is in its off
position and thus the automatic operation is selected, the MPU 43
monitors the rate of a variation in the motor-torque command value.
Here, the rate of a variation in the motor-torque command value
corresponds to the result of differentiating the motor-torque
command value with respect to time. When the monitored variation
rate exceeds a threshold value, the MPU 43 sets the operation mode
to a quicker-torque-response mode in which importance is attached
to torque response. When the monitored variation rate is equal to
or smaller than the threshold value, the MPU 43 sets the operation
mode to a higher-efficiency mode in which importance is attached to
energy efficiency. These processes implemented by the MPU 43
correspond to the operation mode judging means 432.
In the case where the MPU 43 detects that the higher-efficiency
mode is set during the automatic operation, or in the case where
the operation mode selection switch 441 is in its position
corresponding to the higher-efficiency mode during the manual
operation, the MPU 43 calculates a magnetizing-current command
value 401 and a torque-current command value 402, which maximize
energy efficiency, on the basis of the motor-torque command value.
This process implemented by the MPU 43 corresponds to the first
calculating means 433.
In the case where the MPU 43 detects that the
quicker-torque-response mode is set during the automatic operation,
or in the case where the operation mode selection switch 441
assumes its position corresponding to the quicker-torque-response
mode during the manual operation, the MPU 43 fixes the
magnetizing-current command value 401 to a present value thereof
and calculates a torque-current command value 402 from the fixed
magnetizing-current command value 401. These processes implemented
by the MPU 43 correspond to the second calculating means 434. It
should be noted that fixing the magnetizing-current command value
401 to the present value thereof may be replaced by fixing the
magnetizing-current command value 401 to a given value.
The MPU 43 determines voltage command values 403 on the basis of
the magnetizing-current command value 402, torque-current command
value 402, and the measured values represented by the output
signals of the measured value input section 42. This process
implemented by the MPU 43 corresponds to the vector control
calculating means 435. The voltage command values 403 correspond to
desired voltages to be applied to the three-phase ac motor 3.
The switching command signals 404 outputted from the ECU 4 to the
inverter circuit 2 are PWM (pulse width modulation) signals. The
inverter circuit 2 applies different phase voltages to the stator
windings of the three-phase ac motor 3 in response to the switching
command signals 404 respectively. The inverter circuit 2 is of a
PWM type. The switching command signals 404 have voltages which
vary in accordance with patterns corresponding to the
magnetizing-current command value 401 and the torque-current
command value 402.
As previously described, the ECU 4 (the MPU 43) operates in
accordance with a program stored in its internal ROM. FIG. 3 is a
flowchart of a segment of the program which is executed when the
automatic operation is selected.
With reference to FIG. 3, a step s1 of the program segment
calculates a motor-torque command value from the required torque
and the measured values. The required torque is represented by the
accelerator position signal. The measured values are represented by
the output signals of the current detection circuit 30. The step s1
corresponds to the command value calculating means 431.
A step s2 following the step s1 calculates a rate of a variation in
the motor-torque command value. The step s2 decides whether or not
the calculated variation rate of the motor-torque command value
exceeds a threshold value (a given value). When the calculated
variation rate of the motor-torque command value exceeds the
threshold value, the program advances from the step s2 to a step s3
for implementing the quicker-torque-response mode. When the
calculated variation rate of the motor-torque command value does
not exceed the threshold value, the program advances from the step
s2 to a step s5 for implementing the higher-efficiency mode. The
step s2 corresponds to the operation mode judging means 432.
The step s3 fixes a magnetizing-current command value 401 to a
present value thereof. The step s3 corresponds to the second
calculating means 434. Alternatively, the step s3 may fix the
magnetizing-current command value 401 to a given value
corresponding to the motor-torque command value.
A step s4 following the step s3 calculates a torque-current command
value 402 from the fixed magnetizing-current command value 401. The
step s4 also corresponds to the second calculating means 434. After
the step s4, the program advances to a step s6.
The calculation by the step s4 is executed by referring to a
predetermined chart diagram (a predetermined table) indicating a
torque-current command value 402 providing a given motor
torque.
Alternatively, the calculation of the step s4 may be of a direct
type using motor constants.
The step s5 calculates a magnetizing-current command value 401 and
a torque-current command value 402, which maximize energy
efficiency, on the basis of the motor-torque command value. The
step s5 corresponds to the first calculating means 433. After the
step s5, the program advances to the step s6.
The ROM within the ECU 4 stores a predetermined map of FIG. 4 which
provides a relation between a motor-torque command value and a
torque-current command value, and also a relation between the
motor-torque command value and a magnetizing-current command value.
These relations are predetermined on the basis of various factors
such as motor constants, an iron loss, and a copper loss. The
calculation by the step s5 is executed by referring to the map of
FIG. 4.
The step s6 determines voltage command values 403 on the basis of
the magnetizing-current command value 401, the torque-current
command value 402, and the measured values represented by the
output signals of the current detection circuit 30 (that is, the
measured values represented by the output signals of the measured
value input section 42). The voltage command values 403 correspond
to desired voltages to be applied to the three-phase ac motor 3.
The step s6 informs the switching pattern output section 45 of the
voltage command values 403. The step s6 corresponds to the vector
control calculating section 435. After the step s6, the program
returns to the step s1.
As previously described, the switching pattern output section 45
receives information of the voltage command values 403. The
switching pattern output section 45 generates three switching
command signals 404 in response to the voltage command values 403,
and outputs the switching command signals 404 to the inverter
circuit 2. The inverter circuit 2 applies actual voltages to the
three-phase ac motor 3 in response to the switching command signals
404. As a result of the application of the voltages to the
three-phase ac motor 3, a magnetizing current and a torque current
corresponding to the magnetizing-current command value 401 and the
torque-current command value 402 are actually fed to the
three-phase ac motor 3.
As previously described, the ECU 4 (the MPU 43) operates in
accordance with the program stored in its internal ROM. FIG. 5 is a
flowchart of a segment of the program which is executed when the
manual operation is selected (that is, when the manual switch 442
is in its on position).
With reference to FIG. 5, a step s11 of the program segment
calculates a motor-torque command value from the required torque
and the measured values. The required torque is represented by the
accelerator position signal. The measured values are represented by
the output signals of the current detection circuit 30. The step
s11 corresponds to the command value calculating means 431.
A step s12 following the step s11 decides whether the operation
mode selection switch 441 is in its position corresponding to the
quicker-torque-response mode or its position corresponding to the
higher-efficiency mode by referring to the output signal of the
operation mode selection switch 441. When the operation mode
selection switch 441 is in its position corresponding to the
quicker-torque-response mode, the program advances from the step
s12 to a step s13. When the operation mode selection switch 441 is
in its position corresponding to the higher-efficiency mode, the
program advances from the step s12 to a step s15. The step s12
corresponds to the operation mode judging means 432.
The step s13 fixes a magnetizing-current command value 401 to a
present value thereof. The step s13 corresponds to the second
calculating means 434. Alternatively, the step s13 may fix the
magnetizing-current command value 401 to a given value
corresponding to the motor-torque command value.
A step s14 following the step s13 calculates a torque-current
command value 402 from the fixed magnetizing-current command value
401. The step s14 also corresponds to the second calculating means
434. After the step s14, the program advances to a step s16. The
step s14 is similar to the step s4 in FIG. 3.
The step s15 calculates a magnetizing-current command value 401 and
a torque-current command value 402, which maximize energy
efficiency, on the basis of the motor-torque command value. The
step s15 corresponds to the first calculating means 433. After the
step s15, the program advances to the step s16. The step s15 is
similar to the step s5 in FIG. 3.
The step s16 determines voltage command values 403 on the basis of
the magnetizing-current command value 401, the torque-current
command value 402, and the measured values represented by the
output signals of the current detection circuit 30 (that is, the
measured values represented by the output signals of the measured
value input section 42). The voltage command values 403 correspond
to desired voltages to be applied to the three-phase ac motor 3.
The step s16 informs the switching pattern output section 45 of the
voltage command values 403. The step s16 corresponds to the vector
control calculating section 435. After the step s16, the program
returns to the step s11.
As previously described, the switching pattern output section 45
receives information of the voltage command values 403. The
switching pattern output section 45 generates three switching
command signals 404 in response to the voltage command values 403,
and outputs the switching command signals 404 to the inverter
circuit 2. The inverter circuit 2 applies actual voltages to the
three-phase ac motor 3 in response to the switching command signals
404. As a result of the application of the voltages to the
three-phase ac motor 3, a magnetizing current and a torque current
corresponding to the magnetizing-current command value 401 and the
torque-current command value 402 are actually fed to the
three-phase ac motor 3.
A description will now be given of advantages provided by the
above-described embodiment of this invention. Since the manual
switch 442 is provided, selection of one out of the
quicker-torque-response mode and the higher-efficiency mode can be
implemented either manually or automatically in accordance with the
vehicle driver's requirement.
During the automatic operation, when the accelerator pedal 50 is
abruptly or quickly depressed to a considerable degree, the program
in FIG. 3 advances from the step s2 to the step s3 for implementing
the quicker-torque-response mode. Thus, in this case, the step s3
fixes the magnetizing-current command value 401 to the present
value thereof, and the step s4 calculates the torque-current
command value 402 from the fixed magnetizing-current command value
401. Accordingly, the resultant torque-current command value 402 is
made quickly responsive to the change of the accelerator pedal
position. The inverter circuit 2 supplies the three-phase ac motor
3 with a constant magnetizing current and a torque current which
quickly responds to the change of the accelerator pedal position.
Therefore, as shown in FIG. 6, enhanced torque response
characteristics of the three-phase ac motor 3 are available. For
reference, torque response characteristics of a three-phase ac
motor driven by a prior-art apparatus are illustrated in FIG. 7.
According to the embodiment of this invention, the electric vehicle
is quickly accelerated in response to the depression of the
accelerator pedal 50.
During the automatic operation, when the accelerator pedal 50 is
slowly depressed, the program in FIG. 3 advances from the step s2
to the step s5 for implementing the higher-efficiency mode. Thus,
in this case, the step s5 calculates the magnetizing-current
command value 401 and the torque-current command value 402, which
maximize energy efficiency, on the basis of the motor-torque
command value. Therefore, the inverter circuit 2 supplies the
three-phase ac motor 3 with a magnetizing current and a torque
current which correspond to the magnetizing-current command value
401 and the torque-current command 402 respectively. Thus, the
three-phase ac motor 3 and also the electric vehicle are
efficiently operated.
As previously described, the electric vehicle is efficiently
operated in the case where the accelerator pedal 50 is slowly
depressed. On the other hand, in the case where high acceleration
of the electric vehicle is required, the accelerator pedal 50 is
quickly depressed so that the quicker-torque-response mode is
automatically started. Thus, it is possible to meet the requirement
for high acceleration of the electric vehicle.
During the manual operation, when the operation mode selection
switch 441 is in its position corresponding to the
quicker-torque-response mode, the program in FIG. 5 advances from
the step s12 to the step s13 for implementing the
quicker-torque-response mode. Thus, in this case, the step s13
fixes the magnetizing-current command value 401 to the present
value thereof, and the step s14 calculates the torque-current
command value 402 from the fixed magnetizing-current command value
401. Accordingly, the resultant torque-current command value 402 is
made quickly responsive to the change of the accelerator pedal
position. The inverter circuit 2 supplies the three-phase ac motor
3 with a constant magnetizing current and a torque current which
quickly responds to the change of the accelerator pedal position.
Therefore, as shown in FIG. 6, enhanced torque response
characteristics of the three-phase ac motor 3 are available. For
reference, torque response characteristics of a three-phase ac
motor driven by a prior-art apparatus are illustrated in FIG. 7.
According to the embodiment of this invention, the electric vehicle
is quickly accelerated in response to the depression of the
accelerator pedal 50.
During the manual operation, when the operation mode selection
switch 441 is in its position corresponding to the
higher-efficiency mode, the program in FIG. 5 advances from the
step s12 to the step s15 for implementing the higher-efficiency
mode. Thus, in this case, the step s15 calculates the
magnetizing-current command value 401 and the torque-current
command value 402, which maximize energy efficiency, on the basis
of the motor-torque command value. Therefore, the inverter circuit
2 supplies the three-phase ac motor 3 with a magnetizing current
and a torque current which correspond to the magnetizing-current
command value 401 and the torque-current command 402 respectively.
Thus, the three-phase ac motor 3 and also the electric vehicle are
efficiently operated.
As previously described, the electric vehicle is efficiently
operated in the case where the operation mode selection switch 441
is in its position corresponding to the higher-efficiency mode. On
the other hand, the electric vehicle can be quickly accelerated in
the case where the operation mode selection switch 441 is in its
position corresponding to the quicker-torque-response mode. It
should be noted that the operation mode selection switch 441 may be
changed to its position corresponding to the
quicker-torque-response mode when high acceleration of the electric
vehicle is required.
As previously described, the switching command signals 404
outputted from the ECU 4 to the inverter circuit 2 are PWM (pulse
width modulation) signals. The inverter circuit 2 applies different
phase voltages to the stator windings of the three-phase ac motor 3
in response to the switching command signals 404 respectively. The
inverter circuit 2 is of the PWM type. The switching command
signals 404 have voltages which vary in accordance with patterns
corresponding to the magnetizing-current command value 401 and the
torque-current command value 402. Therefore, the three-phase ac
motor 3 can be supplied with a magnetizing current and a torque
current which accurately agree with the magnetizing-current command
value 401 and the torque-current command value 402 respectively.
The accurate agreement between the actual currents and the command
values provides a high control efficiency.
As previously described, the current sensors 311 and 331 detect the
currents flowing along the connection lines 31 and 33 respectively.
The ECU 4 considers the detected currents in the calculation of the
motor-torque command value. Therefore, the available motor-torque
command value is good so that the electric vehicle can travel at a
desired speed.
Second Embodiment
A second embodiment of this invention is similar to the first
embodiment thereof except for the following design changes. The
second embodiment of this invention includes a device for detecting
the amount of electric energy remaining in the vehicle battery 1.
According to the second embodiment of this invention, when the
detected amount of electric energy drops to or below a half of the
maximum amount (corresponding to the fully charged state of the
vehicle battery 1 or the state of the full charge of the vehicle
battery 1), the higher-efficiency mode is forcedly implemented
regardless of the position of the operation mode selection switch
441 or the rate of depression of the accelerator pedal 50.
Third Embodiment
A third embodiment of this invention is similar to the first
embodiment thereof except that the ECU 4 is programmed to provide a
low pass filter processing the magnetizing-current command value
401 during the higher-efficiency mode.
Fourth Embodiment
A fourth embodiment of this invention is similar to the first
embodiment thereof except that the ECU 4 is programmed to provide
low pass filters processing the magnetizing-current command value
401 and the torque-current command value 402 during the
higher-efficiency mode.
Fifth Embodiment
A fifth embodiment of this invention is similar to the first
embodiment thereof except for the following design changes. The
fifth embodiment of this invention is designed for a polyphase ac
motor having independent magnetizing windings. The fifth embodiment
of this invention includes a magnetizing-current feed circuit which
supplies the polyphase ac motor with a magnetizing current
corresponding to the magnetizing-current command value 401.
Sixth Embodiment
A sixth embodiment of this invention is similar to the first
embodiment thereof except that the three-phase ac motor 3 is
replaced by another type of an induction motor, a synchronous
motor, or a reluctance motor.
Seventh Embodiment
A seventh embodiment of this invention is similar to the first
embodiment thereof except for the following design changes. In the
seventh embodiment of this invention, the ECU 4 is programmed to
decide whether or not a magnetizing current to the three-phase ac
motor 3 is low and hence a desired torque is unavailable during the
quicker-torque-response mode.
With reference to FIG. 8, in the case where the ECU 4 decides that
the magnetizing current to the three-phase ac motor 3 is low and
hence the desired torque is unavailable during the
quicker-torque-response mode, a torque-current command value "1"
greater than the present value thereof by a given value starts to
be outputted at a moment t1. Then, at a moment t2, the
torque-current command value is increased to a value "2" while a
magnetizing-current command value remains fixed.
In the seventh embodiment of this invention, an actual torque
current can be increased at a higher rate, and enhanced torque
response characteristics of the three-phase ac motor 3 are
available.
Eighth Embodiment
An eighth embodiment of this invention is similar to the first
embodiment thereof except that the ECU 4 is programmed to provide
low pass filters processing the magnetizing-current command value
401 and the torque-current command value 402.
The eighth embodiment uses a program segment of FIG. 9 instead of
the program segment of FIG. 3. The program segment of FIG. 9
includes a step s7 following the steps s4 and s5. The step s7
subjects the magnetizing-current command value 401 and the
torque-current command value 402 to low pass filtering processes.
After the step s7, the program advances to the step s6.
Ninth Embodiment
A ninth embodiment of this invention is similar to the first
embodiment thereof except for design changes indicated hereinafter.
The ninth embodiment uses a program segment of FIG. 10 instead of
the program segment of FIG. 3.
The program segment of FIG. 10 includes a step s20 following the
step s1. The step s20 detects the voltage across the vehicle
battery 1. It should be noted that the ECU 4 is connected to the
vehicle battery 1 to be powered thereby. The step s20 calculates an
amount of electric energy remaining in the vehicle battery 1 on the
basis of the detected voltage thereacross. The step s20 compares
the calculated amount of remaining electric energy with a threshold
amount. When the calculated amount of remaining electric energy is
equal to or smaller than the threshold amount, the program advances
from the step s20 to the step s5 to implement the higher-efficiency
mode of operation. Otherwise, the program advances from the step
s20 to the step s2.
Tenth Embodiment
A tenth embodiment of this invention is similar to the first
embodiment thereof except for design changes indicated hereinafter.
The tenth embodiment uses a program segment of FIG. 11 instead of
the program segment of FIG. 5.
The program segment of FIG. 11 includes a step s22 following the
step s11. The step s22 detects the voltage across the vehicle
battery 1. It should be noted that the ECU 4 is connected to the
vehicle battery 1 to be powered thereby. The step s22 calculates an
amount of electric energy remaining in the vehicle battery 1 on the
basis of the detected voltage thereacross. The step s22 compares
the calculated amount of remaining electric energy with a threshold
amount. When the calculated amount of remaining electric energy is
equal to or smaller than the threshold amount, the program advances
from the step s22 to the step s15 to implement the
higher-efficiency mode of operation. Otherwise, the program
advances from the step s22 to the step s12.
* * * * *